400 amp service planning row
Common copper planning lookup.
400 kcmil copper or parallel conductorsCommon 400 amp conductor400 amp service wire size
400 Amp Service Wire Size
A 400 amp service is often utility-specific or installed with parallel conductors; this page is only an early planning reference.
Inputs
Results
Immediate estimateCommon 400 amp conductor400 kcmil copper or parallel conductorsVery limited planning lookup; 400 amp services are often engineered, utility-specific, or installed with parallel conductors.
Circuit or service rating400 A
MaterialCopper
Run length75 ft
Voltage dropNot estimated
Acknowledge the limitations before relying on this as a planning lookup.
Electrical sizing depends on the adopted NEC edition, terminal temperature ratings, insulation type, conductor material, conduit fill, derating, grounding, equipment labels, and local inspection requirements.
Diagram
400 amp service
A large service rating returns cautious single or parallel conductor planning language.
- 400 A service
- Material
- Utility review
How this calculator works
Select conductor material and run length for a very limited 400 amp service planning lookup.
Planning row
The engine returns broad single-conductor or parallel-conductor planning language instead of a universal 400 amp prescription.
Why cautious
Large services depend on utility requirements, service equipment, calculated load, conductor configuration, raceway, and inspection rules.
Length flag
Long runs are flagged for voltage-drop review.
Lookup
match amp rating and conductor material to a common residential planning rowLength flag
flag one-way runs over 100 ft for voltage-drop reviewAssumptions
- Lookup scope: Very limited planning lookup; 400 amp services are often engineered, utility-specific, or installed with parallel conductors.
- Not checked: Voltage drop, grounding conductor size, neutral load, service load calculation, conduit fill, ambient temperature correction, bundling, and equipment-specific requirements.
Worked examples
Long aluminum run
Shows voltage-drop caution.
600 kcmil aluminum or parallel conductorsCommon 400 amp conductorFAQ
Is 400 amp service usually parallel conductors?
Often, but not always. The design depends on utility and equipment requirements.
Can I use this for commercial service?
No. This page is U.S. residential planning context only.
Should a 400 amp service be engineered?
Many 400 amp installations need professional design, utility coordination, and inspection review.
Sources and review
- National Electrical Code, NFPA. Accessed 2026-07-16.
- Calculators, Southwire. Accessed 2026-07-20.
Reviewed 2026-07-20. Planning estimates only; confirm project-specific requirements.